Thermostatic control means particularly for electric irons



Nov. 26, 1957 D. J. w. PLlN-r 2,814,711.

THERMOSTATIC CONTROL MEANS PARTICULARLY FOR ELECTRIC IRoNs Filed sept. 1, 1955 3 Sheets-Sheet 1 F/GJ.

Nov. 26, 1957 D. J. w. PLINT 2,814,711

THERMOSTATIC CONTROL MEANS PARTICULARLY FOR ELECTRIC IRONS IFiled Sept. 1, 1955 5 Sheegs-Sheet 2 ANov. 26, 1957 D. J. w. PLINT THERMOSTATIC CONTROL MEANS PARTICULARLY FOR ELECTRIC IRONS Filed Sept. l, 1955 5 Sheets-Sheet 5 THERMOSTATIC CONTRL MEANS PARTICU- LARLY FR ELECTRIC IRONS Dennis John William Plint, Greenford, England, assignor to The Hoover Company, North Canton, Ohio, a corporation of Ohio Application September 1, 1955, Serial No. 531,901

Claims priority, application Great Britain September 6, 1954 16 Claims. (Cl. 219-25) This invention relates to thermostatic control means, particularly, though not exclusively, for electric irons, and an object of the invention is to provide an improved form of adjustable snap-action thermostatic electric switch which lends itself to compact and simple layout suitable for convenient assembly in an electric iron, more especially in the rather restricted `space normally available in a steam iron.

According to the present invention an adjustable thermostatic electric switch includes a pillar, a bimetallic strip anchored to the pillar and having a moving part extending from it in one direction, a snap-action device, a fixed contact supported by the pillar, a moving contact co-operating with the fixed contact and carried by a moving contact arm supported by the pillar and controlled by the snap-action device, the contacts being spaced from the pillar in the opposite direction to the moving part of the hirnetallic strip, an adjusting member supported by the pillar, and a lever operatively connected at one point to the moving part of the bimetallic strip, at another point to the moving contact arm, and at an intermediate point to the adjusting member. Conveniently the pillar includes a hollow sleeve which can be clamped to the sole plate of an iron by a screw passing through it. in one arrangement all the parts of the switch are assembled as a unit on the said hollow sleeve and supported by it. In an alternative arrangement the bimetallic strip is clamped between the `sleeve and the sole plate in direct contact with the sole plate.

The lever may be forked and may have two limbs extending on oppositesides of the pillar. Alternatively, or in addition, the moving contact arm may be forked and may have two limbs extending on opposite sides of the pillar to its anchorage or anchorages. Each limb of the lever may then extend and engage the adjacent limb of the moving contact arm beyond its anchorage.

in one arrangement the moving contact arm is in the form of a spring strip and has two outer limbs in tension and a third central limb arranged in compression so as to constitute the snap-action device.

In one convenient construction the adjusting member includes a screw extending through an arm carried by the pillar. rhe adjusting screw may itself have in it a screw-threaded bore occupied by a pre-adjusting screw which engages the lever to operate it and can be preset, for example to forni a factory adjustment.

The lever may be located by the adjusting member entering a hole in it. in this case turning of the lever about the hole may be prevented by a tongue extending from the arm which supports the adjusting member into a slot in the lever.

They invention may be carried into practice in various ways but one specific embodiment and a modification will be described by way of example with reference to the accompanying drawings in which:

Figure l is a side elevation, partly in section, shownited States Patent O Patented Nov. 26, 1957 Vice ing an electric iron incorporating a thermostatic switch embodying the invention,

Figure 2 is an exploded perspective view showing the main parts of the switch separate from one another,

Figure 3 is a plan view of the switch,

Figure 4 is a sectional side elevation on the line 4 4 of Figure 3,

Figure 5 is a sectional view of the adjusting screw,

Figure 6 is an enlarged detail in section on the line 6--6 of Figure 3, and

Figure 7 is a plan view of a modified form of snapaction device and moving contact arm.

Figure l shows the thermostatic switch embodying the invention incorporated in an electric steam iron comprising a sole plate itl having embedded in it a heating element 11 and having formed in it a boiler 12 from which steam is led through distributing passages, not shown, to ports in the sole plate. A reservoir 13 surmounts the sole plate and is hidden by a cover shell 14. The iron has a handle 15 connected to the cover shell by a front handle pillar 16 and a rear handle pillar i7. Between the handle pillars is a large control dial 18 for adjusting the thermostatic switch, as referred to in detail below. This has in it a central slot 19 and is held in place by a spring clip 20 As shown in Figures 2, 3, and 4, the complete thermostatic switch is built up on and supported by a large hollow rivet 25 so that when assembled it can be bolted to the sole plate Il() of the steam iron by means of a single bolt 26 passing through the centre of the rivet into` a threaded hole in the sole plate. At its lower end the rivet has a large thin flat head 2'7 above which it is encircled in turn by the binietallic strip 2S which extends in one direction which will be referred to as forwards, then by a stop arm 29 carrying a stop for the moving Contact, extending rearwards. Above the stop arm 29 the rivet is encircled by an insulating sleeve 30 which in turn is encircled by an insulating washer 31, tiren by a metal anchoring plate 32, the main part of which extends forwards and sideways to support the moving contact as described below, then by a further insulating washer 34, then by an arm 35 extending rearwards to suppo-rt the fixed contact, then by a further insulating washer 37 and finally by an arm 38 extending forwards to support the main adjusting screw. Above this last arm the end of the rivet 39 is riveted over so as to hold all the parts referred to firmly assembled, as shown in Figures 3 and 4.

The fixed contact arm 35 is of rigid material but has welded to it a short length 4@ of spring strip carrying the fixed contact 41. An adjusting screw 42 extends through the end of the rigid arm and bears on the top of the fixed contact so that the latter can be pressed down more or less by turning the screw. The fixed contact arm also has a lateral lobe 43 to receive a terminal screw for a connecting wire.

The rear part of the moving contact anchoring plate 32 also has a lateral lobe 44 to receive a terminal screw while its forward part carries a moving contact arm 45 in the form of a spring strip of generally E-shape having a central limb 46 in compression, and two outer longer limbs 47 in tension, all connected together by a crosspiece 4S at one end which bears at its centre the moving contact button 50. The free ends of the outer tension limbs 47 extend on opposite sides of the pillar and are rigidly secured as by rivets 49 to the outwardly projecting ends of the anchoring plate 32 at a position forward of the centre of the pillar, as indicated in broken lines in Figure 3. The end of the central compression limb 46 bears in a small obtuse angled V-groove 51 formed in the rearward portion of the anchoring plate, and as shown in Figure 4, is slightly bent so as to be permanently in compression and cause the moving contact to snap rapidly from an open to a closed position and vice versa. In the closed position it bears against the fixed contact 41 above it, whilst in the open position it bears against an insulating stop peg 52. carried in a bore in the end of an adjusting screw 53 fitted into the stop arm 29.

To operate the moving contact, a lever S of generally Y-form is provided. The end 56 of the stem of the lever is bent down rests on the top of the free end of the bimetallic strip 28. The two limbs of the lever are curved to extend round the pillar cn opposite sides of it and each carries an insulating collar 57 bearing upon one of the tension limbs of the moving contact arm at a short distance from its anchorage. As shown in Figure 6 each collar :'57 is held in place on the lever 55 by means of a small spring saddle 59. in the region of the fork of the lever there is a small hole 53 into which projects the end of an adjusting member 6@ whilst the stem of the Y of the lever has in it a longitudinal slot 61 into which projects the downturned end 62 of the arm 38 by which the adjusting member is supported.

The adjusting member comprises a main screw 63 having an external left hand screwthread fitting into a corresponding screwthread in a hole in the supporting arm 38. This main screw has in it a screwthreaded bore to receive a pre-adjusting grubscrew 64 which extends beyond the end of the main screw towards the lever. This pre-adjusting grubscrew has at its end a reduced portion 65 entering the hole 58 in the lever and a shoulder 66 bearing on the upper surface of the lever.

In operation the shoulder at the end of the pre-adjusting grubscrew forms a fulcrum about which the forked lever can pivot. Accordingly if the end of the stem of the forked lever is raised by the end of the bimetallic strip the insulating Collars on its two ends will be lowered and will press down on the tension limbs of the moving contact arm at a short distance from their anchorages. Accordingly after a pre-determined movement, depending on the position of the fulcrum which is determined by the adjusting screw, the moving contact will be rapidly snapped to its open position. As the bimetallic strip cools and moves down the reverse operation will occur and the contact will snap back to its closed position. The position of the fixed contact, and the open position of the moving contact, can be adjusted by means of the adjusting screws and, in addition, the setting of the adjusting member can be pre-adjusted by moving the pre-adjusting grubscrew relatively to the main adjusting screw. In this way a convenient continuous adjustment is available for a facto-ry pre-setting.

The adjusting member 6@ is connected to the control dial 18 by means of a connector 67 in the form of a twisted metal strip whereof the lower end is received in a transverse slot 68 in the screw 63 in which it is retained by a circlip 69, whilst the upper end is received in the slot 19 in the control dial 18.

Figure 7 shows a modified form of snap-action device and moving contact assembly. This comprises an anchoring plate 70 analogous to the anchoring plate 32 of Figures 2 to 6. The anchoring plate '7d supports a moving contact arm '71 comprising two inner tension limbs 72 and two outer compression limbs 73. The ends of the tension limbs are secured as by rivets 74 to the anchoring plate 70 whilst the ends of the compression limbs enter obtuse angled V-shaped grooves in a manner analogous to the central limb 46 of the construction of Figures 2 to 6. As in that construction the tension and compression limbs are inter-connected by a cross-piece 75 carrying the moving contact button Sti.

The operation of the modification shown in Figure 7 is identical to that of the earlier construction. It has the advantage of providing a greater length of compression limb but against this it requires greater accuracy in construction and adjustment.

The whole thermostatic switch is supported by the single pillar and is extremely compactly accommodated around it. It can therefore be fitted into the rather restricted space normally available in an electric steam iron, and moreover the complete switch can be adjusted and tested before being assembled in the steam iron and its assembly in the iron is effected by means of a single screw passing through the hollow rivet constituting the supporting pillar for the mechanism.

In a further modified construction the bimetallic strip is nOt assembled on the rivet 25 but is clamped between the sole plate and the head 27 of the rivet, when the latter is screwed down by the bolt 26. Whilst this arrangement does not permit adjustment of the switch prior to clamping to the sole plate, it may be preferable where accurate temperature control is required since it gives improved heat transfer to the bimetallic strip, the latter being in direct contact with the sole plate.

What I claim as my invention and desire to secure by Letters Patent:

l. An adjustable thermostatic electric switch including a pillar, a bi-metallic strip anchored to the pillar and having a moving part extending from it in one direction, a snap-action device, a fixed contact supported by the pillar, a moving contact co-operating with the fixed contact and carried by a moving contact arm supported by the pillar and controlled by the snap-action device, the contacts being spaced from the pillar in the opposite direction to the moving part of the bimetallic strip, an adjusting member supported by the pillar, and a lever operatively connected at one point to the moving part of the bimetalilc strip, at another point to the moving contact arm, and at an intermediate point to the adjusting member.

2. A thermostatic switch as claimed in claim l in which the pillar includes a hollow sleeve which can be clamped to the sole plate of an iron by a screw passing through it, and all the parts of the switch are assembled as a unit on the said hollow sleeve and supported by it.

3. A thermostatic switch as claimed in claim l in which the pillar includes a hollow sleeve clamped to the soleplate of an iron by a screw passing through it, and the bimetallic strip is clamped between the sleeve and the soleplate in direct contact with the soleplate.

4. A thermostatic switch as claimed in claim l in which the lever is forked and has two limbs extending on opposite sides of the pillar.

5. A thermostatic switch as claimed in claim l in which the moving contact arm is forked and has two limbs extending on opposite sides of the pillar to the anchorage or anchorages.

6. A thermostatic switch as claimed in claim l in which the lever extends, and engages the moving contact arm, beyond the anchorage of the latter.

7. A thermostatic switch as claimed in claim l in which the moving contact arm is in the form of a spring strip and has a set of limbs comprising at least one outer limb, and a set of limbs comprising at least one inner limb, whereof one set is in tension whilst the other is in com-pression, so as to constitute the snap-action device.

8. A thermostatic switch as claimed in claim l in which the adjusting member includes a screw extending through an arm carried by the pillar.

9. A thermostatic switch as claimed in claim 8 in which the adjusting screw itself has in it a screwthreaded bore occupied by a pre-adjusting screw which engages the lever to operate it, and can be pre-set.

l0. A thermostatic switch as claimed in claim 8 in which the lever is located by the adjusting member cntering a hole in it.

ll. An adjustable thermostatic electric switch including a pillar, a bimetallic strip anchored to the pillar and having a moving part extending from it in one direction, a snap-action device, a xed contact supported by the pillar, a forked moving contact arm supported by the pillar and controlled by the snap-action device and having two limbs extending on opposite sides of the pillar and anchored at their ends, a moving contact carried by the opposite free end of the moving Contact arm and cooperating with the xed contact at a point spaced from the pillar in the opposite direction to the moving part of the bimetallic strip, a forked lever operatively connected to the moving -part of the bimetallic strip and having two limbs extending thence on opposite sides of the pillar beyond the anchorages of the moving contact arm and engaging the limbs thereof, and an adjusting member supported by the pillar and operatively connected to the lever at a point intermediate the connections of the latter to the bimetallic strip and moving contact arm.

12, A thermostatic switch as claimed in claim 11 in which the pillar includes a hollow sleeve which can be clamped to the sole plate of an iron by a screw passing through it, and all the parts of the switch are assembled as a unit on the said hollow sleeve and supported by it.

13. A thermostatic switch as claimed in claim 11 in which the pillar includes a hollow sleeve clamped to the sole plate of an iron by a screw passing through it, and the bimetallic strip is clamped between the sleeve and the soleplate in direct contact with the soleplate.

14. A thermostatic switch as claimed in claim 11 in which the moving contact arm is in the forni of a spring strip and has a set of limbs comprising at least one outer limb, and a set of limbs comprising at least one inner limb, whereof one set is in tension whilst the other is in compression, so as to constitute the snap-action device.

15, A thermostatic switch as. claimed in claim 11 in which the adjusting member includes a screw extending through an arm carried by the pillar.

16. A thermostatic switch as claimed in claim 15 in which the adjusting screw itself has in it a screw-threaded bore occupied by a preadjusting screw which engages the lever to operate it, and can be pre-set.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,864 Weber Nov. 8, 1938 2,287,787 Dickey June 30, 1942 2,417,161 Hanner Mar. 11, 1947 FOREIGN PATENTS 474,472 Italy Sept. 24, 1952 

